The specific goals we propose are to assess qualitative and quantitative changes in immune responses to filarial antigens from the time when previously unexposed individuals arrive in an endemic area until they develop clinical and/or parasitological manifestations of lymphatic filariasis. Methods include quantitation of circulating T cell subclasses; functional assessment of T cells (by antigen induced in vitro proliferation assays), and of B lymphocytes (by assays detect in vitro production of specific antibody to B. malayi); measurement of antifilaria antibody of different classes and isotypes as well as of circulating immune complexes; and analysis of parasite antigens recognized during the course of filarial infections (by Western blots with sera from donors with differing periods of exposure). The ultimate goal is to identify parasite antigens that elicit immune reactions with prognostic significance that could be included in a potential vaccine against lymphatic filariasis in man.